Many handling problems may arise when one is forced to prepare aqueous end-use formulations and/or slurries from solids, especially active solids, e.g. wettable bioactive powders as is often the situation in the agricultural industry. Farmers preparing tank mixes of herbicides, insecticides and/or other bioactives from solids for applications to crop and soil are exposed to certain safety hazards and inconveniences due to the generation of noxious dusts which may be irritable to the skin and hazardous to breathe.
Additionally, finely ground powders, even so-called powders, of many water-soluble bioactives when prepared as tank mixes do not disperse well, they have poor spontaneity or "bloom" and have low suspendability, they have poor re-dispersibility and are incompatible with other bioactives as compared to liquid bioactive concentrates. Thus, final formulators, such as farmers, when preparing diluted aqueous active compositions find that the handling and application of solids materials such as fertilizers, are much facilitated if the material can be supplied in a fluid rather than solid form. Economics then dictates that the active material be supplied in a highly concentrated fluid to the final formulator.
Saturation solubility in water of many water-soluble active constituents, such as ammonium nitrate, is too low to make it economical to supply it to the end-user simply in the form of a solution. Alternatively, highly concentrated suspensions of water soluble compounds, both in water and in organic liquids, have very poor storage, freeze/thaw, and heat/cool stability.
As a result of the spontaneous crystal dissolution-recrystallization process, there occurs a progressive increase in the size of the particulate active material. This increase in particle size results in settling, bleed and changes in visco-elastic properties and thus severely limits concentrate loading levels.
The instant invention concerns a unique formulation which, to a great extent, addresses and overcomes the above problems.
Particle size stability of water-soluble particulate solids is obtained in a twofold manner. First, by appropriate selection of the organic carrier used as the continuous phase, the temperature coefficient of solubility can be controlled, thus stabilizing the particle size of the solids throughout usual commercial storage times and temperature cycles. The major component of the carrier liquid is non-aqueous, although small amounts of water may be used to modify the performance. Secondly, recognizing that a small number of large particles has a smaller total surface area than a large number of small particles regardless of morphology, the surface-free energy of the active solid material is lowered via surfactant adsorption onto the particle surface, thus reducing the necessity to obtain a minimization of the surface area which promotes growth of the particles.
The particle size stability and other desirable characteristics of the concentrate such as low viscosity, minimum syneresis and high bloom are primarily controlled through the use of a three component surfactant system.
The first component, a nonionic viscosity-improver material, preferably a polymeric material and most preferably an ethylene oxide-propylene oxide block copolymer, is primarily used, through rheology control, to create a stable dispersion and secondarily to mollify crystal growth.
The second component, an anionic surfactant, preferably a sulfonate, albeit having a syneresis-increasing influence, is utilized primarily to synergistically reduce the viscosity enhancing effect of the polymeric first component and secondarily, as a result of its affinity for the surface of the solids, to aid in the dispersibility of the solid particles.
The third component, which is a bulky nonionic surfactant containing a large hydrophobic group, preferably an ethoxylated tristyryl phenol such as Soprophor BSU.RTM. (Rhone-Poulenc Inc., Cranbury, N.J.), is primarily used to reduce the packing of the particles, i.e., it reduces syneresis or settling and serendipitiously enhances the bloom or dispersibility that occurs when the concentrated composition is diluted by pouring it into an aqueous medium to achieve the final concentration of the end-use formulation.
This third component also has a tendency to increase the viscosity of the concentrate.
Optionally, a minor amount of water may be added to the concentrate primarily to assist in adjusting the temperature coefficient of solubility which ultimately minimizes changes in particle size.
U.S. Pat. No. 5,082,591 to Marchetto, et al. discloses emulsifiable concentrated solutions of herbicides, pesticides, and other active agricultural compounds comprising a polyoxyethyleneated/polyoxypropylenated (1-phenylethyl) phenol as the surfactant. The compositions also contain a wetting agent, a stabilizing agent and a second nonionic, cationic, or amphoteric surfactant. The compounds enable agricultural actives to have improved shelf life stability, are stable in water and enable the production of highly concentrated solutions for ease of handling and transport.
U.S. Pat. No. 4,393,151 to Dowans, et al. teaches stabilized suspensions of water soluble polymers in a liquid hydrocarbon medium including a thickening agent consisting of the alkaline earth metal salts of fatty acids having from 6-33 carbon atoms. The suspensions dissolve readily in water and actively disperse. They are allegedly useful in enhanced oil field recovery. U.S. Pat. No. 3,960,742 to Leonard discloses corrosion inhibitor compositions comprised of a ethylene glycol monoalkyl ether solvent, inorganic alkaline solids dispersed therein and small amounts of two or more surfactants as suspension agents. The compositions are highly concentrated yet shelf stable and very effective in the removal of grease, oil, tar, asphalt, etc. from all surfaces. The concentrate is also non-flammable, ecologically benign and relatively non-toxic.
U.S. Pat. No. 4,265,406 to Palgrave, et al. discloses the use of an additive such as a polysaccharide to at least partially inhibit regrowth at crystal surfaces when comminuting concentrated solid materials such as water soluble explosives or fertilizer salts in saturated solutions.
Through use of the organic carrier and surfactant systems of this invention, exceptionally high loadings, i.e., from about 40 to 85% by weight of the total weight of the composition, of suspensions of water-soluble solids are prepared which exhibit minimal changes in particle size and are characterized by settling and visco-elastic properties that produce suspensions which are extremely stable even under long term storage conditions.